1. Field of the Invention
The present invention relates to an image display system, in particular, an image display system in which an image display device performs overdrive processing.
2. Description of the Background Art
With regard to a conventional liquid crystal display device, there has been well known the following disadvantage. That is, upon display of a moving image, a moving image blurring phenomenon occurs due to a factor of motion of a liquid crystal molecule, a factor of a drive method (hold type display) by which a single image is displayed continuously during one frame period, or the like.
The factor of the motion of the liquid crystal molecule is caused by the following two reasons. One of the reasons is that the liquid crystal molecule moves slowly due to its viscosity. The other reason is that in a case where the liquid crystal display device is driven by an active element such as a TFT (Thin-Film Transistor), a direction of a liquid crystal at a point in time when a pixel is charged varies after a while, resulting in variation in dielectric constant of the liquid crystal and variation in effective voltage. In order to deal with the phenomenon occurring due to this factor, the conventional liquid crystal display device adopts an overdrive processing technique.
Herein, overdrive processing refers to a technique of using information about a state of a liquid crystal at a point in time when a pixel is charged and information about an image to be displayed subsequently, in order to apply a voltage for bringing, to an optimum state, motion of the liquid crystal during a period that the liquid crystal is charged and then is charged again.
In order to deal with the phenomenon occurring due to the factor of the hold type display, on the other hand, the conventional liquid crystal display device adopts various techniques such as a blinking backlight method by which a backlight shut-off period is provided, a black insertion method by which a black display period is provided, and a frame interpolation and high-speed drive method by which an image between original image frames is generated and displayed at a frequency faster than a frame frequency of an original image.
As another drive method, the liquid crystal display device also adopts a field sequential drive method by which red backlight, green backlight, blue backlight and the like are emitted sequentially to change display by the liquid crystal display device from monochrome display to color display in a timeshared manner. As still another drive method, the liquid crystal display device also adopts a directivity scan backlight method by which backlight having special directivity is emitted sequentially in a specific direction and then the liquid crystal display device is driven in a timeshared manner in synchronization with the emission of the backlight to display an image which changes depending on a direction of view or to display a three-dimensional image. However, these methods are not pertain to solution of the problem of the moving image blurring phenomenon.
In the frame interpolation and high-speed drive method, the field sequential drive method or the directivity scan backlight method, the liquid crystal display device is driven at a high speed with respect to a frame cycle (normally, about 60 Hz) of an original image. In other words, when the liquid crystal display device is driven at a high speed, the frame period becomes short. Consequently, the liquid crystal molecule must be moved in a desired direction within the frame period. In order to satisfy this request, the liquid crystal display device frequently adopts the overdrive processing together with the foregoing drive method.
Japanese Patent Application Laid-Open Nos. 2004-304390 and 2003-143556 disclose examples of an image display device that adopts the overdrive processing.
In order to perform the overdrive processing, the image display device must grasp a state of a liquid crystal molecule at a point in time when a pixel is charged. Herein, the image display device requires at least information about image data in a preceding frame or information about a state of the liquid crystal molecule in the preceding frame. In order to determine an optimum drive voltage, alternatively, the image display device holds plural pieces of information over plural frame periods rather than information in one frame. That is, in order to perform the overdrive processing, the image display device requires at least information in a preceding frame and, therefore, must be provided with a frame delay circuit having a frame memory.
For example, input image data is inputted to each of a frame delay circuit and a LUT (Look Up Table). Based on the received input image data and the input image data sent from the frame delay circuit, the LUT generates and outputs image data corresponding to a predetermined applied voltage. Occasionally, the LUT obtains the image data by a function rather than a table. Moreover, the LUT changes a value of the image data depending on an ambient temperature.
Herein, consideration is given to an image display system including an image display device that includes an overdrive processing circuit and an image generation device that generates image data and transfers the image data to the image display device. The image generation device, which generates image data, includes a graphic memory. The graphic memory is used for rendering graphics, image data sent from a camera or a scanner, received broadcast video, and the like. The image display system described above requires two memories, that is, the graphic memory in the image generation device and a frame memory in the image display device, leading to increase in cost as a whole.
In each of image display systems disclosed in Japanese Patent Application Laid-Open Nos. 2004-304390 and 2003-143556, an image generation device has an overdrive processing function. Thus, the image display system allows reduction in memory cost as a whole. Herein, each of the image display systems disclosed in Japanese Patent Application Laid-Open Nos. 2004-304390 and 2003-143556 performs interlace-progressive conversion.
Frequently, the image generation device and the image display device are manufactured by different makers, respectively. In each of the image display systems disclosed in Japanese Patent Application Laid-Open Nos. 2004-304390 and 2003-143556, if the maker of the image display device is changed, setting values for the overdrive processing must be adjusted. In order to make fine adjustment such as change in setting values for overdrive processing depending on temperature, preferably, the image display system has a configuration that the image display device has the overdrive processing function, unlike the image display systems disclosed in Japanese Patent Application Laid-Open Nos. 2004-304390 and 2003-143556.